South Korea's SK Telecom begins SIM card replacement after data breach

SK Telecom announced earlier this month that it had fallen victim to a hacking incident involving malicious code, through which customers' personal information was compromised.

It prompted a company apology and the government to order the review of the country's overall data protection system.

SK Telecom has not given details on the extent of the damage or who was behind the attack.

"Starting from 10 am (0100 GMT) on Monday, we will replace USIM chips free of charge for those who wish to replace them at 2,600 carrier stores nationwide," the company said in a press release on Monday.

USIM stands for Universal Subscriber Identity Module, used in mobile networks.

The company has vowed to take full responsibility and asked users to sign up for an information protection service.

"We will also thoroughly prepare for the USIM replacement, so please visit a store," it said.

But it has acknowledged that it has secured less than five percent of the USIM cards needed for its 23 million-strong customer base, noting it will procure additional five million chips by the end of May.

"I wish they had been more transparent about how much information had been leaked and how many subscribers were affected," said Jang, who was waiting in line in central Seoul to get a new chip.

"But instead, they have only told us to either change our USIM chips or sign up for a protection service," the 30-year-old company worker said, asking to be identified by his surname.

South Korea, widely recognised as among the most wired country in the world, has long been a target of cyber hacking by North Korea, which has been blamed for several major attacks in the past.

Police announced in May that North Korean hackers were behind the theft of sensitive data from a South Korean court computer network -- including individuals' financial records -- over a two-year period.

The stolen data amounted to more than one gigabyte in size.